Physics – Geophysics
Scientific paper
Nov 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980e%26psl..51...94m&link_type=abstract
Earth and Planetary Science Letters, Volume 51, Issue 1, p. 94-114.
Physics
Geophysics
8
Scientific paper
Oxic siliceous clay and calcareous ooze cores from the central North Pacific were analyzed for 232Th, 231Pa and 230Th activities, and for organic carbon contents to establish Late Quaternary sedimentation rates and organic carbon decomposition rates during early diagenesis. High excess activities revealed Late Quaternary deposits in the upper sections of all cores but one. Sedimentation rates for the youngest phase of continuous deposition were between 3.2 and 5.8 mm/1000 yr for calcareous ooze and between 1.5 and 4.1 mm/1000 yr for siliceous clay.
The ionium decrease with depth revealed characteristic discontinuities in five sediment cores, also shown by other parameters. The discontinuities date back to 15,000-100,000 years B.P. and are associated with pronounced facies changes in four cores. One core contained siliceous clay (1.9 mm/1000 yr) covered by more rapidly accumulating calcareous ooze (5.8 mm/1000 yr). In three siliceous clay cores the discontinuity marked the facies I/II boundary of von Stackelberg [31].
Fixed ammonium distributions in the sediment cores, reflecting varying amounts of illite, were used in lithostratigraphic correlations. Ages of around 1.3 million years, estimated by extrapolation of sedimentation rates to greater depths, suggest that the facies I/II boundary is equivalent to the Quaternary/Pliocene boundary in areas of continuous Quaternary (facies I) sedimentation.
All sediments were typically low in organic carbon, i.e. less than 0.4 wt.%. Concentrations decreased exponentially with depth showing the same discontinuities as the ionium distribution. Organic carbon contents, however, reached constant carbon/alumina ratios of between 0.005 and 0.007 at depths of about 1 m below the surface. Thus small amounts of organic matter (i.e.<0.1%) appear to resist decomposition probably due to being sorbed to clay minerals.
First-order decay constants of metabolizable organic carbon ranged from 3.2 × 10-6 to 27.5 × 10-6 yr-1, corresponding to half-lifes between 217,000 and 25,000 years. Rate constants were found to be proportional to the 1.5th power of the sedimentation rate similar to the relationships established for anoxic sediments by Toth and Lerman [43] and Berner [44]. However, the constants derived here are higher by about three orders of magnitude if extrapolated to comparable sedimentation rates used by the cited authors. This probably reflects the higher efficiency of organic matter decomposition under oxygenated conditions.
Our results suggest a sedimentation rate threshold of >1 to <4 cm/1000 yr below which the chemical environment remains oxic in pelagic regions of moderate productivity. Metabolizable organic matter is completely remineralized within 150,000 to 450,000 years after burial, assuming 4 half-lifes and sedimentation rates of 4 and 2 mm/1000 yr, respectively. This corresponds to sediment dephts <1 m below the interface and explains the prevailing oxic conditions of pelagic biogenic oozes and clays at greater depths.
Present address: Department of Geology and Geophysics, Yale University, New Haven, CT 06520, U.S.A.
Mangini Augusto
Müller Jan-Peter
No associations
LandOfFree
Organic carbon decomposition rates in sediments of the pacific manganese nodule belt dated by 230Th and 231Pa does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Organic carbon decomposition rates in sediments of the pacific manganese nodule belt dated by 230Th and 231Pa, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Organic carbon decomposition rates in sediments of the pacific manganese nodule belt dated by 230Th and 231Pa will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1390820